This invention relates to pipelines, and particularly to an oil transportation pipeline especially adapted for use transporting petroleum over long distances offshore in an arctic environment.
Because of the large petroleum resources available offshore Alaska, a great deal of research and study has been undertaken in recent years in order to determine whether it would be feasible to construct an oil pipeline extending offshore. A pipeline buried under the bottom of the ocean has its own inherent problems, perhaps the most significant of which is the effect of pipeline temperature on the permafrost under the ocean. Permafrost is frozen soil, much of which contains large quantities of frozen water. Its strength is dependent upon the frozen condition of its water content. Thus, if melting occurs, the permafrost may no longer provide support. Oil, on the other hand, only flows efficiently at relatively high temperatures, its viscosity varying adversely with the temperature. Furthermore, at high flow rates, oil temperature may actually increase in the pipeline. An ordinary pipeline buried in permafrost would transmit heat to the permafrost, Even if adequate support remained, the application of heat by the pipeline to the permafrost over a long period of time would cause a pool of water to collect which would continue to grow into a large pond or "thaw bulb", possibly causing a great deal of damage to the pipeline and to the environment.
Accordingly, it is desirable in the art to provide an arrangement of insulating, thermally absorbing and/or dissipating elements controlling heat flow between a pipeline and its environment. The insulating elements also should serve to maintain relatively stable temperature differentials between heated materials in the pipeline and adjacent ground support, so that there is a minimal effect of one on the other.